Borrelia burgdorferi, the etiologic agent of Lyme disease, is the most frequent arthropod borne infection in the United States. Despite the information obtained from the genome sequence, very little is understood regarding how this bacterium responds to the distinct niches it occupies in nature (arthropods and mammals) and no regulatory systems have been molecularly defined. The investigators long-term goal is to understand how B. burgdorferi modulates gene expression in response to environmental signals and to link this knowledge to the synthesis of specific molecules that contribute to pathogenesis. The objectives of this application are to characterize an oxygen-specific regulatory network and relate its role to the expression of genes important in the life cycle of B. burgdorferi. The hypothesis is that dissolved oxygen is an important cue that B. burgdorferi uses to sense its environment and mobilize a response via the regulatory locus perR. PerR is a metallo-regulatory protein that modulates the expression of genes involved in the oxidative stress response. B. burgdorferi perR mutants are resistant to hydrogen peroxide, suggesting that PerR represses expression of redox responsive genes in B. burgdorferi. The investigators also determined that the perR mutant is de-repressed in additional genes unrelated to the stress response, suggesting that PerR constitutes a regulon. The investigators propose to characterize the PerR regulon with the following Specific Aims: (1) Identify the genes that comprise the PerR regulon. The investigators will use a genomic and proteomic based approach to determine genes regulated by PerR in response to the redox status; (2) Determine the mechanism of PerR regulation. PerR binds metals and may be redox responsive. The investigators propose to determine which co-factors modulate PerR activity; and (3) Relate proteins regulated by the redox status of cells to in vivo expression, and protective immunity. Several antigens are upregulated in perR mutants and when oxygen levels are low. PerR regulated antigens expressed during periods of oxidative stress and repressed when oxygen is limiting will be tested as protective immunogens. The investigators predict that the PerR regulon is important for both the physiology and pathogenesis of Lyme borreliosis as it modulates the expression of genes required for resistance to toxic oxygen species and factors required for adhesion, respectively.